Field of the Invention
The present invention relates to a vibration-type actuator and an optical device using this, and in particular, relates to a technique to miniaturize a vibration-type actuator and to stabilize its drive state.
Description of the Related Art
A vibration-type actuator generally has an electro-mechanical energy conversion element, a vibration body in which drive vibration is excited by the element, and a driven body that is in pressure contact with the vibration body, and moves the vibration body and the driven body relatively by drive vibration. FIG. 11A is a perspective view schematically showing a configuration of the vibration-type actuator 110 of a well-known linear type.
The vibration-type actuator 110 has a tabular vibration body 111, first and second projections 112 on one side of the vibration body 111, a piezoelectric device 113 that is an electro-mechanical energy conversion element attached to the other side of the vibration body 111, and a driven body (not shown) that is in pressure contact with the projections 112. It should be noted that a three-dimensional orthogonal coordinate system is set up for description as shown in FIG. 11A. An X-direction connects the two projections 112, and is a relative moving direction of the vibration body 111 and the driven body here. A Z-direction is a thickness direction of the vibration body 111, and a Y-direction is perpendicular to both of the X- and Z-directions. Accordingly, the piezoelectric device 113 is adhered on the X-Y plane of the vibration body 111.
FIG. 11B and FIG. 11C are views for describing two bending vibration modes that are drive vibrations generated in the vibration body 111 by applying drive voltage to the piezoelectric device 113. One bending vibration mode (hereinafter referred to as an “A-mode”) shown in FIG. 11B is a quadric curvature movement in the X-direction in which three nodes parallel to the Y-direction appear. The projections 112 are arranged near the positions of the nodes in the vibration in the A-mode, and reciprocate in the X-direction by the vibration in the A-mode.
The other vibration mode (hereinafter referred to as a “B-mode”) shown in FIG. 11C is a linear flexing vibration in the Y-direction in which two nodes parallel to the X-direction appear. The projections 112 are arranged near the position of antinodes in the vibration in the B-mode, and reciprocate in the Z-direction by the vibration in the B-mode.
The vibration-type actuator 110 generates elliptic motion or circular motion at the top ends of the projections 112 by generating the vibrations in the A-mode and B-mode at predetermined phase difference. At this time, the driven body is in pressure contact with the top ends of the projections 112 on the vibration body 111 by a pressurizing means (not shown). Accordingly, friction drive force is given to the driven body in the X-direction, and the vibration body 111 and the driven body move relatively.
There is a known method to press the driven body against the projections 112 with attraction force of a magnet arranged at the back side (the side of the piezoelectric device 113) of the vibration body 111 as an example of a method by which the driven body is in pressure contact with the projections 112 (see Japanese Laid-Open Patent Publication (Kokai) No. 2011-239571 (JP 2011-239571A)).
However, the method to press the driven body against the projections 112 using the magnet as described in the above-mentioned publication needs a thick magnet in order to obtain sufficient pressure force when the projected area of the magnet viewed in the Z-direction is small. Accordingly, there is a problem that it is not easy to attain a miniaturization. Moreover, when the projections 112 are small, the pressure force may not be stabilized and sufficient driving force may not occur because the attraction force also operates between the vibration body 111 and the driven body.